Defined Benefit and Other Postretirement Benefits - Plan Assets Measured at Fair Value (Details) - Trustmark Capital Accumulation Plan [Member] - Trustmark Corporation Pension Plan for Certain Employees of Acquired Financial Institutions [Member] - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Asset target allocations [Abstract]
Fair value of plan assets	$ 3,954	$ 4,596	$ 54,734
Level 1 [Member]
Asset target allocations [Abstract]
Fair value of plan assets	3,954	4,596
Level 2 [Member]
Asset target allocations [Abstract]
Fair value of plan assets	0	0
Level 3 [Member]
Asset target allocations [Abstract]
Fair value of plan assets	0	0
Money Market Funds [Member]
Asset target allocations [Abstract]
Fair value of plan assets	304	269
Money Market Funds [Member] | Level 1 [Member]
Asset target allocations [Abstract]
Fair value of plan assets	304	269
Money Market Funds [Member] | Level 2 [Member]
Asset target allocations [Abstract]
Fair value of plan assets	0	0
Money Market Funds [Member] | Level 3 [Member]
Asset target allocations [Abstract]
Fair value of plan assets	0	0
Exchange Traded Equity Securities Funds [Member]
Asset target allocations [Abstract]
Fair value of plan assets	2,044	2,199
Exchange Traded Equity Securities Funds [Member] | Level 1 [Member]
Asset target allocations [Abstract]
Fair value of plan assets	2,044	2,199
Exchange Traded Equity Securities Funds [Member] | Level 2 [Member]
Asset target allocations [Abstract]
Fair value of plan assets	0	0
Exchange Traded Equity Securities Funds [Member] | Level 3 [Member]
Asset target allocations [Abstract]
Fair value of plan assets	0	0
International Exchange Traded Funds [Member]
Asset target allocations [Abstract]
Fair value of plan assets	444	666
International Exchange Traded Funds [Member] | Level 1 [Member]
Asset target allocations [Abstract]
Fair value of plan assets	444	666
International Exchange Traded Funds [Member] | Level 2 [Member]
Asset target allocations [Abstract]
Fair value of plan assets	0	0
International Exchange Traded Funds [Member] | Level 3 [Member]
Asset target allocations [Abstract]
Fair value of plan assets	0	0
Exchange Traded Fixed Income Funds [Member]
Asset target allocations [Abstract]
Fair value of plan assets	1,162	1,462
Exchange Traded Fixed Income Funds [Member] | Level 1 [Member]
Asset target allocations [Abstract]
Fair value of plan assets	1,162	1,462
Exchange Traded Fixed Income Funds [Member] | Level 2 [Member]
Asset target allocations [Abstract]
Fair value of plan assets	0	0
Exchange Traded Fixed Income Funds [Member] | Level 3 [Member]
Asset target allocations [Abstract]
Fair value of plan assets	$ 0	$ 0